The present invention relates to an electric machine comprising a rotor and a stator arranged coaxially therewith, at least one of said rotor and stator being formed of a plurality of parts and there being provided a bandage holding together the plurality of parts of said rotor and/or stator.
The present invention in general relates to the simplification of the construction and manufacture of electric machine, in particular electric motors and generators having internal or external rotors composed of individual parts as well as stators composed of individual parts, respectively. These individual parts, in conventional manufacture, are joined together using mechanically positive or form-fit connections, for example screws or mutually engaging parts etc. This kind of connection is complex in terms of working and assembly. Furthermore, there is the fact that some materials, in particular materials used for the permanent magnets, are relatively difficult to work.
A bandage circumferentially enclosing the individual parts is a suitable alternative to such mechanical positive connections. The bandage encloses the individual parts and holds the same together. The bandage is basically capable of withstanding relatively high forces, especially the centrifugal forces arising with a rotor. The bandage may optionally also be provided in combination with mechanical positive connections for retaining the individual parts.
The bandage provided on the outer circumference of the stator or rotor, however, increases the diameter thereof to a not insubstantial extent. Especially with internal rotors in which the bandage is arranged in the air gap between rotor and stator, the thickness of the bandage has a decisive effect on exploitation and efficiency of the electric machine. The designing engineer strives to keep this air gap as small as possible. Even if the air gap can be reduced by just a tenth of a millimeter, this has considerable effects on the power and efficiency of the machine. Because of the known high strength of carbon fiber materials, carbon fiber material was thus used to make the bandages. In case of electric machines of usual size, the thickness of this bandage is typically between 0.5 and 5 mm, which is already inadmissibly large for some applications. In this context, it is to be pointed out in particular that this problem does not only exist with such electric machines in which the bandage is disposed in the air gap between rotor and stator, but also in case of such electric machines in which the bandage is arranged on the outer circumference, e.g. around the outside of the external rotor. In this event, the thickness of the bandage results in a greater overall diameter of the electric machine, which may also be undesirable for some applications.
The object of the present invention thus consists in reducing the thickness of the bandage of known electric machines of the type indicated hereinbefore.